$\begingroup$if I am sampling a current that has a frequency of 25 KHz and my sampling rate is 30 Hz, does this mean i cannot detect signals in my current that have a frequency higher than 15Hz?$\endgroup$
– MehdiMay 4 '16 at 8:27

$\begingroup$How does it answer the question?$\endgroup$
– jojek♦May 4 '16 at 8:27

$\begingroup$Mehdi : yes. If you do a FFT in the conditions you are explaining, you will not be able to reconstruct the 25 Hz signal if the initial data had a 30 Hz sampling rate. @Jojek : That is what I understood from Mehdi's question : "Is this sampling rate the same as the frequency used when calculating the FFT when creating the frequency axis of the FFT?" means for me "Is this sampling rate the same as the frequency axis of the FFT". From Mehdi's answer above it seems to me that it was the kind of information he was looking for. If not, Mehdi maybe you can clarify the question ?$\endgroup$
– AdrienPMay 4 '16 at 8:59